In recent years, communication that utilizes a human body as a portion of a signal transmission line is drawing attention; and a biological communication device has been proposed in which an electromagnetic field is generated between a signal electrode and ground and propagates via the human body surface. However, because the spacing between the signal electrode and ground becomes narrow when downsizing and reducing the thickness of the communication device, the capacitance of the signal electrode becomes high; the return loss increases; and communication becomes difficult.